NATIONAL GEOGRAPHIC ANSWER BOOK FAST FACTS ABOUT OUR WORLD

WHAT IS A VIRUS?

A virus is a microscopic infectious generate nor store energy on their SMALLPOX IS CAUSED when variola vi- 149
agent that enters animal, plant, or own. In fact, viruses depend on host rus particles (above) enter the cells of a host.
bacteria hosts. A single virus particle, cells for all their metabolic functions. Extinct since 1977, smallpox is maintained in »z
called a viron, is little more than a cultures by the U.S. and Russia for research.
bundle of genetic material-DNA or Some scientists decline to count Ul
RNA- that does not take the form viruses among living organisms, since many kinds of viruses. Antibiotics can-
of a cell. Instead it is encased in a shell they cannot survive on their own not cure viral illnesses, but vaccines can ~
called a viral coat, or capsid, made of and cannot reproduce outside of a prevent them, and many widespread
bits of protein. Some viruses have an host cell. Not usually counted among life-threatening viral outbreaks, such m
additional enclosure around the capsid plants, animals, or prokaryotic bacte- as smallpox, have been controlled or
called an envelope. ria, viruses are instead classified in a eliminated with vaccines. ;;D
group of their own.
Viruses cannot function without ooOJ
their hosts. They cannot synthesize pro- What viruses can do, however, is
teins without essential ingredients from infect, or cause disease. Fortunately, A
their host cells, and they can neither the immune systems of most animal
species can fend off infection from »OJ

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LOUIS PASTEUR I PIONEER MICROBIOLOGIST

Louis Pasteur (1822-1895) earned four university degrees by the time he was 25. As

dean of a new science program at the University of Lille, France, he created evening
classes for factory workers and included industrial applications of science. He also

started his own experiments on fermentation in alcohol and milk. Moving in 1867

into a laboratory of physiological chemistry set up for him by Emperor Napoleon
III, Pasteur began to tackle the question of spontaneous generation: Did organisms
grow spontaneously from certain substances, such as maggots from dead flesh or
weevils from wheat? Knowing fermentation was hastened by exposure to air, Pasteur
proved that microbes in the air caused putrefaction. He invented the process named
after him, pasteurization, which destroys harmful microbes so food can be stored.

" I am persuaded that life, as It IS known to us, IS a direct result of

asymmetry of the universe. - LOUIS PASTEUR, 1874

FAST FACT The amoeba moves by its pseudopod, or false foot, the most primitive form of animal locomotion.

":OR MORE -ACTS ON

CHALLENGE OF PROVIDING SAFE FOOD FOR WORLD see Food. CHAPTER 6, PAGES 244·5, & Agriculture: Modern. CHAPTER 6, PAGES 248·9

+

ATTENTION TO VIRUSES IN MEDICAL SCIENCE see Medicol Science. CHAPTER 8, PAGES 338·9

w rthropods, the phylum of animals that includes
insects, spiders, and crustaceans, represent 84
5 percent of all animal life on the planet. More
than one million species of creeping, crawl-
l/) ing, and flying creatures are included in the
order, and they inhabit every continent and biome through-
z out the world-in and on the ground, in the water, and in the
sky. And scientists are identifying new species all the time.
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All arthropods, including insects, are and six legs. Many insects also have
ODONATA I Dragonflies invertebrates-they have no back- antennae and wings. Most insects
DICTYOPTERA I Cockroaches & mantids bones. Insects have exoskeletons hatch from eggs and undergo some
ORTHOPTERA I Grasshoppers & crickets (outside skeletons) made of chitin, form of metamorphosis, or life cycle
a light, flexible material containing transformation. Often metamorphosis
ISOPTERA I Termites protein. An insect has a three-part involves molting, the shedding of a too-
HEMIPTERA I True bugs body-head, thorax, and abdomen- small exoskeleton as the insect grows.
COLEOPTERA I Beetles
SIPHONAPTERA I Fleas

DIPTERA I Flies
LEPIDOPTERA I Butterflies & moths
HYMENOPTERA I Ants, bees & wasps

FAST FACT A square mile of field may be home to almost six billion insects.

FOR MORE FACTS ON

CLASSIFICATION OF LIVING THINGS see Ufe-forms. CHAPTER 4, PAGES 132·3

+

THE CHARACTERISTICS & LIFE CYCLES OF BUTTERFLIES & MOTHS see Insects: Butterflies & Moths. CHAPTER 4, PAGES 152·3

Beetles form the most numer- People often use the words "bug" tip. Their rear wings are thin and clear, 151
ous insect group, with about 350,000 and "insect" interchangeably, but in and their wings fold over their backs in
known species. Hard-bodied with fact, bugs are a particular kind of in- a characteristic X shape. »z
firm front wings that protect their sect and make up only about 10 per-
bodies and rear wings, beetles typi- cent of all insects. They usually have Spiders are not insects but arthro- Vl
cally morph from egg to larva to pupa front wings that are thick and hard pods, as are centipedes, millipedes,
before attaining the adult stage. near the body, thin and clear at the ticks, and mites. Worms form a differ- ~
ent group altogether-the annelids.
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WHERE ARE ALL THE BEES? z

In October 2006, U.S. beekeepers be- factors: hive overcrowding or poor Vl
gan noticing that they were losing some nutrition. Researchers have also found
30 to 90 percent of the populations of that pollution can reduce the range of a m
their hives. The phenomenon has be- flower's scent by 75 percent- another
come known as colony collapse disor- possible factor in colony collapse. ()
der. An affected hive will still have a live
queen and often some honey and some The loss of honeybee hives could --I
immature bees, but no adult worker severely affect U.s. agriculture, es-
bees are to be found, dead or alive. pecially the production of nuts and Vl
other orchard crops, where bees are
Possible causes include pesticides, used to promote pollination, which HONEYBEES are social insects, living in
the appearance of a new parasite or guarantees an abundant crop. In areas
pathogen, or a combination of stress affected by colony collapse disorder, colonies that number in the tens of thou-
sands of individuals.

growers are trucking in hives of unaf-
fected bees from long distances to ac-
complish pollination.

FAST FACT The trap-Jaw ant snaps shut Its mandibles 2,000 times faster than the blink of an eye.

• HOW OLD ARE COCKROACHES?

Most insects descend from long, virtually identical in shape and size to
hardy lineages. One of the most today's pests. One coal mine in east-
durable is the cockroach, which has ern Ohio contained fossil specimens
changed very little in more than 300 not only of cockroaches with three-
million years. Fossils from the Paleo- inch wings but also of centipedes,
zoic era (left) include cockroaches millipedes, and spiders.

Ii. • • ... • • ••

":OR MORE -ACTS ON

SPIDERS see Spiders & Their Kin, CHAPTER 4, PAGES 154-5

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PREHISTORIC LIFE ON EARTH see Ages of the Earth, CHAPTER 3, PAGES 94-5, & Ufe Begins, CHAPTER 4, PAGES 130-1

BUTTERFLIES & MOTHS

B152 utterflies and moths belong to consuming plant matter, then undergo their wings closed, while moths usually
I the order Lepidoptera, which metamorphosis into the adult forms. hold theirs out flat. Also, moth bodies
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means "scale wings." Butter- There are several ways to tell a are usually plumper than those of the
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flies and moths fly with two pairs of butterfly from a moth. On the whole, butterfly. In the pupal stage, a butterfly
oz wings covered with tiny, overlapping, butterflies are brightly colored whereas makes a smooth, shiny chrysalis, while

W powdery scales that often rub off. moths are more drab. Butterflies flut- a moth makes a woolly cocoon.
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--' Almost all butterflies and moths ter about in the day, but moths tend The feeding habits of moths can

a:: have a long, tubular mouthpart called to be nocturnal. Butterflies have knobs prove destructive to the natural and

o::J a proboscis, which they use to feed on the ends of their threadlike anten- human-constructed world. The larvae
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on plant nectar. They spend their lar- nae; moth antennae are wider and of- of the European pine shoot moth have
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I- val stage as caterpillars, voraciously ten feathery. At rest, butterflies keep devastated large swaths of pine for-

«0.. ests there by eating the tree's tender
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fabric made from plants and animals,

oOL such as cotton and wool, making holes
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in clothing and carpets.
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5 have shown the role of pheromones,
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the opposite sex across a large number

of animal species. Even the male silk

moth, a domesticated species used in

silk production that has only stumpy,

flightless wings, demonstrates the al-

lure of these potent chemicals.

In one famous experiment, a male

is alerted of a female's presence by

the airflow of an ordinary household

fan. As soon as the scent reaches the

male's antennae, he beats his stubby

wings and runs-since flying is not an

option-toward the female to mate

with her. A pheromone-laced piece of

MONARCH BUTTERFLIES commune at a watering hole in central Mexico, preparing for their paper can produce the same effect.
long annual migratory flight north.

FAST FACT The atlas moth, found in Asia's tropical regions, has a wingspan of 8 to 12 inches.

FOR MORE FACTS ON

INTERESTING ANIMAL MATING BEHAVIOR see Animal Curiosities, CHAPTER 4, PAGES 170·1

+

THE VARIETY AND HISTORY OF TEXTILES IN HUMAN CULTURE see Clothing, CHAPTER 6, PAGES 242-3

THE YUCCA CONNECTION

Of the many plant-animal connections in the natural world, A FEMALE YUCCA MOTH seeks nectar on the tip of a stamen 153
that of the yucca plant and the yucca moth is one of the inside a fragrant yucca flower, one step in the complex symbiosis be-
most specialized. These species have evolved a relationship tween plant and insect. »z
in which one depends on the other for survival: Only the
yucca moth can pollinate the plant, whose seeds provide Vl
the moth's only food source.
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the yucca flowers . When the caterpillars hatch, they feed m
on some of the seeds. Those remaining seeds grow into the
next generation of yucca plants. Meanwhile, the caterpillars ;;D
drop off the plant and pupate in the cocoon stage in soil,
transforming into the next generation of yucca moth. The ooOJ
moths that emerge begin the process all over again.
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FROM CATERPILLAR TO BUTTERFLY Mothsandbutterfliesundergoamatu-
rational transformation so remarkable OJ
THE TIGER SWALLOWTAIL, like all moths and butterflies, assumes three forms after it has become the stuff of myth and
it hatches from an egg: larva (or caterpillar), chrysalis, and mature insect. The entire process poetry around the world. C
takes about one month. Moths undergo a similar metamorphosis. --I
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tive covering made by a moth caterpillar from its own silk in which it rests and transforms into an adult moth.

":OR MORE -ACTS ON

THE DIVERSITY OF LIFE-FORMS ON EARTH see Biodiversity, CHAPTER 4, PAGES 174-7

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THE HUMAN TRADITION OF TELLING MYTHS AND LEGENDS see Language, CHAPTER 6, PAGES 228-9

w ithin the arthropods, spiders occupy a
taxonomic class called the arachnids,
5 a group comprising a diverse array of
other creatures including mites, ticks,
l/) and scorpions. The horseshoe crab
IS closely related as well. Arachnids have a two-part body
z and eight legs. Spiders in particular have silk glands and use
the contents to spin webs and to encase their eggs or prey.
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Most spiders produce venom and squirting it with digestive juices before
ACARI /Mites & ticks inject it into their prey through one sucking up the mushy contents.
AMBLYPYGI / Whipscorpions pair of mouthparts, the chelicerae,
which act like fangs. The other pair The pedipalps in scorpions have
ARANEAE / Spiders of mouthparts, called pedipalps or developed into claws. Scorpions also
OPILIONES / Daddy longlegs pincers, are used to sense prey. have stingers at the end of their tails
PALPIGRADI / Micro-whipscorpions and use them to inject highly toxic
PSEUDOSCORPIONES / False scorpions Tenacious predators, spiders and venom into their prey. Scorpions oc-
other arachnids are unable to ingest cupy crevices and burrows during the
SCORPIONES / Scorpions prey whole and must liquefy it by day and come out at night to hunt.
SOLIFUGA E / Wind scorpions, camel

spiders, sun spiders
U ROPYGI / Whip-tai led scorpions.

vinegaroons

FOR MORE FACTS ON

THE DIVERSITY OF PLANT & ANIMAL SPECIES see Biodiversity, CHAPTER 4, PAGES 174-7

+

THE CONCEPT OF NATURAL HABITAT OR BlOME see Biomes, CHAPTER 5, PAGES 194-5

Mites and ticks occur In almost of arthropods and represent some Some crustaceans live on land,
every habitat. Many of these abun- 39,000 species that display a wide but most live in salt or fresh water.
dant species are parasites, feed- variety of features. Lobsters, crabs, Their heads usually sport two pairs
ing on the fluids of other animals. and shrimp are the most well known of antennae, stalked eyes, and three
Crustaceans belong to a subphylum of the group. pairs of biting mouthparts.

FAST FACT South Amenca's tarantula, up to 12 Inches across. eats Insects. frogs. bats. rodents. and even baby birds. 155

VARIETIES OF SPIDERWEBS »z

Spiders create webs by extruding silk from glands. Some specialized for a dragline, a web frame, an egg case, and Vl
spiders have as many as seven specialized glands, each other purposes. Spiders can be classified according to the
of which manufactures a different protein-rich silk strand type of web they weave. ~

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ORB WEBS are circular in pattern. SHEET WEBS spread out in flat planes. FUNNEL WEBS include a hole for hiding.

FAST FACT Of the world's some 40.000 spider species. only about 30 have venom that causes illness In humans.

HORSESHOE CRABS: LIVING FOSSILS

A close relative of the spider-and and can also travel along the mud by MALE HORSESHOE CRABS converge
not a crab at all- the horseshoe crab pulling up their body and pushing with on a single female during early June, breeding
bears a long lineage. Vestiges of simi- the spine and rear legs. season on the New Jersey shoreline.
lar animals date back 200 million years.
Horseshoe crabs have hinged bodies, Spring tides bring horseshoe crabs
a horseshoe-shaped head, and a long onto the land by the thousands. Fe-
tail-spine. They can grow up to two males scoop out depressions in the
feet long. They live on the east coasts sand and fill them with hundreds of
of Asia and North America. eggs. Males follow and cover the eggs
with sperm. Within two weeks tiny
Horseshoe crabs feed on true hatchlings, about an eighth of an inch
crabs, mollusks, worms, and other long, wash out to sea with the tide to
prey. They swim along the ocean floor complete their life cycle.

":OR MORE -ACTS ON

EARTH'S OCEANS & THEIR TIDES see Water: Oceans, CHAPTER 3, PAGES 114-5

+

THE EVOLUTION OF PREHISTORIC LIFE-FORMS in Lire Begins, CHAPTER 4, PAGES 130-1

GIANT SQUID

Architeuthis species
660 inches (estimated)

GIANT CLAM

Tridacna gigas
5 1 inches

AUSTRALIAN TRUMPET SNAIL

Syrinx aruanus
30 inches

SEA SLUG

Hexabranchus sanguineus
20 inches

HETEROPOD

Carinaria cristata
19 inches

STELLER'S COAT OF MAIL SHELL

Cryptochiton stelleri
18 inches

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5 he beautiful seashells collected by people the and tentacles; the smaller end admits
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world over are actually protective coverings water to breathe and removes waste.
<{ Octopuses, squid, cuttlefish, and

for a vast array of invertebrates known as nautiluses, also mollusks, are called

mollusks. A mollusk is an animal covered in a cephalopods (literally, head feet).

thin layer of tissue called a mantle, which pro- Their feet are located close to their
duces a calcium carbonate shell. Mollusks occur in varied heads in a modification of tentacles.
Among these animals, only the nautilus

habitats, sea and land, from ocean bottom to mountaintop. has a full shell. The squid and cuttlefish

have a shell remnant inside the body.

Typical shelled mollusks divide into foot that it uses to pull itself along and The octopus has no shell at all.

four categories: bivalves, chitons, gas- to cling to surfaces. Cephalopods are predators that

tropods, and tusk shells. Gastropods (which means "stom- also scavenge. They draw food into

Bivalves, such as oysters, clams, ach feet"), the largest mollusk group, their mouths and crush it with their

and mussels, have a two-part hinged include snails, slugs, and limpets. Most sharp, parrotlike beaks. Cephalopods

shell. Most burrow into sediment and have a spiral shell, but some, such as travel by means of jet propulsion.

some attach to a firm surface. slugs, have no exterior shell. They squirt water from their bodies to

Chitons are oval in shape and have Tusk shells have a long, tubelike move forward and back. The octopus

an interlocking eight-part upper shell. shell that is open at both ends. The deftly manipulates its eight suctioned

Most of a chiton's body is a single, flat larger end contains the foot, head, tentacles to travel.

FOR MORE FACTS ON

THE OCEANS OF PLANET EARTH see Oceans. CHAPTER 3, PAGES 112-5

+

PLANTS & ANIMALS IN UNDERWATER LIVING ENVIRONMENTS see Aquatic Biomes. CHAPTER 5, PAGES 212-3

HOW SMART ARE CEPHALOPODS?

Three cephalopods- octopus, squid, 157
and cuttlefish-have shown appar-
ently deliberate, cunning, and even »z
subversive behavior, causing even the
most skeptical researchers to take Vl
notice. All three have demonstrated
puzzle-solving abilities, a capacity for ~
boredom that can be relieved by mak-
ing up games, and the ability to deceive m
prey, fellow members of their species,
and even their keepers in order to get ;;D
what they want.
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ums have been known to dismantle A
the pumps in their tanks and to use
amazing escape techniques to sneak o,3-:
out at night, visit other tanks and gorge
on fish, and then be back in place by ,-
daybreak, having left behind a telltale
watery smear on floor and walls. c

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SQUID LOCOMOTION occurs thanks to a mantle, a flap of tissue surrounding its head. In
slow motion, the mantle helps the squid stabilize and turn. For quick moves, the squid effects a
watery sort of jet propulsion, sucking in water, locking the mantle shut, and then spewing the
water out in a focused stream. Squid can swim backward or forward.

NAUTILUS: NATURE'S PERFECT GEOMETRY

Related to the squid, the octopus, and
the cuttlefish, the nautilus is the only
cephalopod with an exterior shell.
The shell starts out with only a few
chambers. The animal itself resides in
the innermost chamber. As the animal
grows, new chambers are added, al-
ways following the same proportion.
The resulting spiral of the nautilus
shell closely approximates the golden
mean, a ratio of I: 1.618.

NAUTILUS POPULATIONS concentrate
in the tropical West Pacific. They are now
endangered, primarily because their shells are
prized by collectors and curio purchasers.

FAST FACT Giant clams embed themselves in the seafloor and never move; they can weigh up to 700 pounds.

":OR MORE -ACTS ON

HUMAN METHODS OF LOCOMOTION see Transportation. CHAPTER 6, PAGES 252·3

+

THE IMPORTANCE OF PROPORTIONS IN MATHEMATICAL THINKING in Counting & Measurement. CHAPTER 8, PAGES 322-3

«Vz> ish account for more than half of all the vertebrate
species known in the world, with more than 24,000
ATLANTIC BLUEFIN TUNA species identified so far. They are found in almost
CHILEAN SEA BASS every watery habitat-salt, fresh , or brackish-
GROUPER from large puddles to polar seas. They range in size
ORANGE ROUGHY from gobies, less than an inch long, to whale sharks, 59 feet
ATLANTIC COD long. Fish come in all colors and in thousands of patterns, but
ATLANTIC HALIBUT some are colored drably to blend in with their surroundings.
SNAPPER
SHARK Fish fall into three main groups: jaw- Most fish have scales that pro-
less, cartilaginous, and bony. The tect their bodies. Nearly all fish have
category of jawless fish includes hag- fins, used for swimming. Flying fish
fish and lampreys; the category of can launch themselves into the air for
cartilaginous fish includes sharks and brief periods, and some fish, such as
rays; and the category of bony fish, walking catfish, use their fins to drag
to which the largest number of fish themselves along on land.
belong, includes both the lobe-finned
and the ray-finned fish species. Most fish reproduce by means of
eggs laid by the female and fertilized

WATER & OCEANS ON PLANET EARTH see Water, CHAPTER 3, PAGES 110·9
UNDERWATER LIVING ENVIRONMENTS see Aquatic Biomes, CHAPTER 5, PAGES 212-3

by the male, outside the female's body. Many fish eat algae or insect lar- Fish frequently travel in large
Many sharks, however, reproduce by vae and other small animals, but some, groups called schools or shoals. Using
internal fertilization and live birth from such as sharks, are tireless predators low-frequency sonar, researchers de-
the mother's body. that hunt even large sea mammals. tected a shoal of some 20 million fish.

HOW DO FISH BREATHE? 159

flE5PtRATORY Most fish breathe with gills, arched into the bloodstream. The filaments »z
SYSTEMS structures on either side of the and lamellae also dump carbon diox-
OFFISH Vl

body that contain features known as ide from the body into the gills, and ~

filaments and lamellae. Water, which water carries it out of the body. Many m

contains oxygen, flows in through the species, including sharks and bony fish, ;;D
fish's open mouth and then out across have a pumping mechanism that aids
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the gills. Rakers filter out particles as respiration.

_ - - - - 6rKt1On of the water flows through. A fish out of water suffocates be-

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Blood coursing through the fila- cause its gill structures collapse and the
ments and lamellae delivers oxygen oxygen exchange cannot continue.

. .. .. .:......

THE LIFE STORY OF A SALMON

Every sockeye salmon undertakes a more than any other salmon. Then, SOCKEYE SALMON, third most abundant
life journey with distinctive changes in called smolt, they make a transition to of seven Pacific salmon species, may swim 600
form and location. One of the smaller salt water. They stay in the ocean for miles upriver to reach their spawning grounds.
species of Pacific salmon, the sockeye one to four years.
is also called the red or blueback salm-
on. "Sockeye" is an early mispronun- Finally they return upriver to
ciation of a Native American name. breed. Seagoing sockeyes have silver
flanks with black speckles and a bluish
The adult female lays her eggs in top, but as they return to their spawn-
river gravel. When the eggs hatch, the ing grounds, their bodies turn bright
nourishing yolk sac remains attached red and their heads take on a green-
to the young fish. Within a few days, ish color. Breeding-age males have a
the fish consume the attached yolk sac distinctive look, developing a humped
and become free-swimming fry. back and hooked jaws filled with tiny,
easily visible teeth . Males and females
Juvenile sockeyes will stay in their both die a few weeks after spawning.
natal habitat for up to three years,

FAST FACT Some kinds of fish change sex multiple times to increase chances of reproductive success.

":OR MORE -ACTS ON

THREATS TO EARTH'S WATERY ENVIRONMENTS see Threatened Planet: Water. CHAPTER 3, PAGES 126·7

+

THE FUTURE OF FISH & FISH FARMING see Agriculture: Modern. CHAPTER 6, PAGE 249

COLUBRIADAE o
1,700 species I 1-10 feet long; many spe-
cies lay eggs I Includes garter snakes, corn ..e,!
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snakes, black snakes, rat snakes
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BO IDAE
45 species I 3-25 feet long; bear living r0-
young I Includes pythons, boas, and
an
anacondas
8g,
ELAP IDA E
315 species I 2-20 feet long; venom- F
conducting fang; may bear live young or
lay eggs I Includes cobras, mambas, coral .c..,:...

snakes, taipans 08
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VI PERIDAE
260 species I 1- 12 feet long; eye with
vertical pupil ; movable jaw bones; venom-
injecting fang that folds against roof of
mouth I Includes rattlesnakes, vipers,
adders, copperheads, water moccasins

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5 eptiles form an ancient line of vertebrates that lived for a century or more in captivity.
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have lived on Earth for more than 300 million Many sea turtles take between 20 and
<{ 40 years to reach sexual maturity.

years. They include four main groups: crocodil- Generally, reptiles do not need

ians, snakes, lizards, and turtles. Cold-blooded to eat as often as birds and mammals.

animals, reptiles most commonly inhabit the They may go for days, even weeks,

without food. Flexible jaws enable

world's temperate and tropical regions, in salt and fresh snakes to ingest prey that is much

water, on and under the ground, and in trees . A few spe- wider around than they are.

cies live in the Arctic and survive by sunning themselves All snakes are carnivores, and some
for warmth. Reptiles in very hot climates often remain In are aggressive predators with venom-
ous bites. Venom potency varies. In

the shade or underground during the day. some snake species the venom merely

stuns prey; in others it kills quickly.

Like mammals and birds, reptiles engage young or even feed them; most are long A few lizard species, such as the Gila

in internal fertilization. In most spe- gone by the time the eggs hatch. monster, also have a venomous bite.

cies, the female lays eggs after fertiliza- Turtles are renowned for their A rare, fifth type of reptile, the

tion, but some snakes give birth to live longevity. The American box turtle is tuatara, is the last of a large group of

young. Although female crocodiles are known to live up to 30 years, and some beak-headed reptiles that lived before

caring mothers, few reptiles raise their giant tortoises are reported to have the dinosaurs.

FOR MORE FACTS ON

EQUATORIAL & TROPICAL REGIONS OF THE WORLD see Dividing Unes: Equator & Tropics. CHAPTER I, PAGES 36·7

+

PLANTS & ANIMALS IN THE DESERT BIOMES see Desert & Dry Shrub/and. CHAPTER 5, PAGES 208·9

HOW DO SNAKES MOVE?

Snakes may lack arms and legs, but hold the ground as the muscles pull the
their supple bodies squeeze through
narrow openings and slither- a mo- snake forward . Snakes move accord-
tion that depends on the combina-
tion of a flexible spinal column, strong ing to the terrain they travel through.
muscles, and specialized scales on
their undersides called scutes. Sidewinding snakes in sandy habitats

Adult humans have 26 vertebrae have ways to keep from slipping: The 161
in their spines; a snake may have more
than 400. Each pair of ribs is attached snake swings its head and upper body »z
to a vertebra. Overlapping scutes on
the snake's belly attach by muscles to forward and sideways. Its lower body Vl
the animal's ribs.
and tail follow, with the belly raised ~
When the snake is moving, the
back edges of the scutes catch and above the hot sand, leaving a J-shaped m

pattern in the sand . ;;D

Some snakes climb trees. To do ooOJ

that, a snake coils up like an accordion, A

anchors with its tail , then stretches its SNAKE SPINES are long and supple, thanks ;;D
head forward, gathering momentum, to the large number of vertebrae they contain,
so the rest of the body catches up. more than any other vertebrate. m

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CROCODILE OR ALLIGATOR?

Crocodilians can be distinguished by ing swamps and rivers, alligators are
the shapes of their snouts and jaws. brownish gray.
Crocodile teeth line the entire jaw-
line and are visible even when their Crocodillian species inhabit all the
mouths are closed. They inhabit salt- world's continents except Europe.
water environments. Their color tends They are carnivores, but their diets vary
toward olive green. Alligator teeth by species and surroundings. Croco-
cluster in the front of the jaw and dis- diles and alligators are known to eat
appear when the animals' mouths are insects, slugs, snails, and crustaceans
shut. Freshwater creatures, inhabit- frequently, but birds and small mam-
mals also sometimes fall prey to them.

CROCODILES AND ALLIGATORS, both reptiles, can be distinguished through a few key
observations, particularly the V-shaped snout of the crocodile (top) compared with the U-shaped
snout of the alligator (bottom).

FAST FACT In 2006 a Komodo dragon in an English zoo laid a fertile egg without its being fertilized by a male.

":OR MORE -ACTS ON

DEFINITION & GEOGRAPHY OF RIVERS see Water: Rivers. CHAPTER 3, PAGES 116-7

+

CLASSIFICATION OF ANIMAL & PLANT SPECIES see Life-forms. CHAPTER 4, PAGES 132-3

162 oz

I r;:\

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LL m0-

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a:: 3

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a::
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vertebrates to leave the water and live on
I- • land. The name amphibian means "double
life," and most amphibians live part of their
«"- lives in water and part on land. Amphibians
reproduce from eggs, which are usually laid in water. They
I hatch in a larval stage and breathe through gills before trans-
U forming into air-breathing adults that live mostly on land.

OL Amphibians have scaleless skin kept and salamanders, and legless creatures
moist by mucus glands. Many spe- called caecilians.
oo t--I'J cies breathe through the skin, even
though they have lungs for breathing, Frogs form the largest group of
cD too. The skin of some amphibians amphibians. They differ from toads by
produces toxins that thwart preda- having longer and more slender bod-
a:: tors or even kill them. ies, being better jumpers, and having
smoother, moister skin. Frogs were
w There are three main groups of the first land animals with vocal cords,
amphibians: frogs and toads, newts and their songs still punctuate many
5

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COLOMBIA I 209 species

MEXIC O I 196 species

ECUADO R I 162 species

BRAZIL I 110 species

CHINA I 88 species

PERU I 8 1 species

GUAT EMALA I 76 species

VENEZUELA I 69 species

INDIA I 66 species

COSTA RICA I 6 1 species

FOR MORE FACTS ON

HOW ANIMALS BREATHE THROUGH GILLS see Fish, CHAPTER 4, PAGE 159

+

PLANTS & ANIMALS IN THE RAIN FOREST BlOME see Forests: Rain Forests, CHAPTER 5, PAGES 198·9

an evening around the world. Strictly quite secretive. Most species emerge Legless caecilians look like worms
speaking, toads are frogs, but there is from eggs laid underwater. They then and are the only amphibians with
a family called true toads. transform to gilled larvae, spend a ter- scales, found underneath their skin.
restrial phase as efts, and head back to Most are blind and live underground,
Salamanders and newts, the sec- the water as adults to breed. excavating with their hard heads.
ond largest group of amphibians, are

• • •• 163

WHERE DO DART FROGS GET THEIR POISON? »z

Poison dart frogs inhabit the rain venom for hunting, spreading a tiny Vl
forests of Central and South America. amount on a dart that they propel by
Their brilliant colors make them look blowgun into their prey. ~
like children 's playthings, but they
represent some of the most naturally Scientists suspect that poison dart m
toxic animals on Earth. Humans have frogs gain their toxicity from alkaloids
learned to make use of their poison. in the food they eat, including ants ;;D
and mites. Poison dart frogs raised
The golden poison dart frog, for in captivity and isolated from their ooOJ
example, grows only two inches long native diet do not develop venom.
but contains enough venom to kill ten A
human beings. The Embera people HARVESTING POISON for hunting, a Co-
of western Colombia use this frog 's lombian native touches the tip of his arrow to »
the body of a colorful golden poison dart frog.
3:

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ENDANGERED AMPHIBIANS

Amphibians-frogs in particular-are creases the tadpoles' vulnerability. THE GOLDEN TOAD, once native to Costa
considered a bellwether of environ- More amphibian species have Rica but now extinct, may have succumbed to
mental health. Recent reports from climate change as rain forest mist dwindled
many locations tell of frogs with ex- been disappearing since the I970s, over the highland forests near Monteverde.
tra limbs, misplaced limbs, and other too. Kihansi spray toads, for example,
abnormalities occurring at a higher inhabit only ten acres in Tanzania's
rate than expected. Many research- Kihansi River gorge. When a new
ers lay blame on a parasite infection dam there diverted 90 percent of
and pesticide runoff. water flow in 2000, the toad popula-
tion began to plummet. Today these
Frog tadpoles pick up parasites toads- along with other endan-
in ponds where infected snails live. gered species- are being nurtured in
The parasites form hard cysts in the captivity in zoos, with the idea that
tadpoles' bodies and interfere with populations could eventually be rees-
limb development. Pesticide runoff in- tablished in the wild.

FAST FACT Dart frogs have only one predator: a snake, Lelmodophls epmephelus, that is Immune to their poison.

":OR MORE -ACTS ON

ENDANGERED ANIMAL SPECIES see Biodiversity: Threatened Species, CHAPTER 4, PAGES 178-9

+

THE GEOGRAPHY & ECONOMICS OF COLOMBIA see South America, CHAPTER 9, PAGE 426

CALIFORNIA CONDOR
Raised in captivity, reintroduced
into wild, numbers slowly increasing

WHOOPING CRANE
W ild popu lation slowly increasing

GUNNISON SAGE-GROUSE
Popu lation estimated 2,000-6,000

KIRTLAND'S WARBLER
Cowbirds disturb nests; human contro ls

improving situation

PIPING PLOVER
Human activities dist urb beach nesting

FLORIDA SCRUB-JAY
Numbers declined preCipitously

in the 20th century

w

5 irds descended from dinosaurs more than 150 mil- Many bird species migrate. Most

l/)
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lion years ago. Like their reptile ancestors, birds have move in and out of winter and sum-
<{ mer ranges to take advantage of fa-

scales on their legs and lay eggs. Unlike dinosaurs, vorable weather and food supplies,

birds are warm-blooded. The recent discovery of but some take this to the extreme,
featherlike fibers preserved in amber for 100 million traveling thousands of miles between
years raises the question of whether dinosaurs had feathers or destinations.

Birds originally were grouped

whether these ancient feathers came from flightless birds. by morphology: their outward form
and features. Today, studies of bird

There are about 10,000 bird species the kiwi, and the ostrich-have lost DNA support much of this classifica-

worldwide. Scientists continue to find the ability to fly over the course of tion but give a truer picture of bird

previously undiscovered species even their evolution. evolution and relationships.

as other species face extinction. Birds range in size from the Bird morphology, however, still

Most birds are built aerodynami- ostrich-nine feet tall and 300 remains the key to identification

cally, with bullet-shaped bodies, mus- pounds-to the bee hummingbird, among the vast numbers of people

cular wings, and lightweight bones. which measures two inches and worldwide who enjoy birdwatching

Some birds-such as the penguin, weighs a mere tenth of an ounce. as a pastime.

FAST FACT The alarm call of the Southern Screamer, related to ducks and geese, can be heard two miles away.

FOR MORE FACTS ON

MIGRATORY HABITS AMONG ANIMALS see Migration, CHAPTER 4, PAGES 172-3

+

EXTINCT ANIMALS INCLUDING DINOSAURS see Biodiversity: Extinction, CHAPTER 4, PAGES 176-7

THE NATURAL HISTORY OF BIRDSONG

Birdsong is an exceedingly complex songs. Birds sing to defend territory MIGRATORY SONGBIRDS of North Amer- 165
and sophisticated communication and to attract mates. Some species ica, including the Baltimore oriole (top), the rose-
system. It is produced from the bird's even sing when pursued by predators breasted grosbeak (lower left), and the whip- »z
syrinx, a sound box at the junction of to convey how robust they are. On the poorwill (lower right), are declining in number.
the two bronchi, which lead to the whole, males sing more than females. Vl
lungs. Air from the lungs is passed The male brown thrasher has com-
over membranes in the syrinx, which mand of some 2,000 different songs. ~
then vibrate, producing sound waves. Male and female birds sometimes sing
Because there are two bronchi with duets, and groups of birds may sing to- m
membranes, sound can emanate from gether to defend a territory.
each and combine higher in the vo- ;;D
cal tract, producing a large variety of Some species are especially ad-
sounds. ept at mimicry. Some Scottish star- ooOJ
lings reproduce the sounds of sheep;
Complexity in the vocal muscles some English starlings even mimic A
also translates into more complex city buses.
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IDENTIFYING BIRDS ~~~-------------- crown

____ ___ ___ _ ___ ___ ___ _ ___ ___ __~~~~::~r------------- nbaapcek

chin r--------

There are millions of bird-watchers throat tail

in the world-people who look for,

identify, and catalog bird species. breast ------------------------------Y
Some participate in organized events,
competing and mutually cataloging side -------------------------------+- ~~~~
their observations. Many keep life lists,
recording all the birds they have seen belly ---------------~
secondary wing feathers ------------------------>....,...-'I<~

over the years. To confirm a bird's

identity, bird-watchers note the distinc-

tive appearance of certain body parts. tertial wing feathers ---------------------------¥---"---------'

primary wing feathers

":OR MORE -ACTS ON

BIOLOGICAL CLASSIFICATION SYSTEMS see Ufe-forms. CHAPTER 4, PAGES 132·3

+

THE HUMAN IMPULSE TO SING & MAKE MUSIC see Music. CHAPTER 6, PAGES 240-1

«Vz> ammals are vertebrates distinguished by their
ability to produce milk to feed their young.
AFRICAN ELEPHANT I 660 days They grow hair-sometimes a full-body cov-
ASIATIC ELEPHANT I 600 days ering of fur and sometimes just a few whis-
BAIRD'S BEAKED WHALE I 520 days kers here and there. Mammals are typically
WHITE RHINOCEROS I 490 days considered warm-blooded, although the naked mole rat,
an African species, may present an exception to this rule.
WALRUS I 480 days
GIRAFFE I 460 days Mammals are divided into three large There are about 5,000 species of
groups based on methods of repro- mammals, which evolved from reptiles
TAPIR I 400 days duction: monotremes, marsupials, and some 200 million years ago. Rodents
DROMEDARY I 390 days placental mammals. Monotremes lay represent almost half of these species.
FIN WHALE I 370 days eggs, marsupials give birth to underde-
veloped young that mature in a pouch Mammals live on the land and
LLAMA I 360 days of skin on the mother's abdomen, and underground, in the air, and in both
placental mammals give birth to devel- salt and fresh water. They inhabit all
oped young that are nourished during the continents except Antarctica, al-
gestation by a placenta. though even there, marine mammals
live in surrounding waters.

WATER·DWELLING MAMMALS see Sea Mammals, CHAPTER 4, PAGES 168·9
A DEFINITION OF THE BlOME AS GEOGRAPHIC UNIT OF NATURE ON EARTH see Biomes, CHAPTER 5, PAGES 194·5

PRIMATE KIN

Primates as a group are intelligent, A BONOBO, also called a pygmy chimpanzee--the primate most closely resembling a hu- 167
largely tree-dwelling mammals with man-mirrors his keeper at play in the ABC Sanctuary of the Democratic Republic of the Congo.
forward -looking eyes that allow them »z
to see in three dimensions. They pos-
sess opposable thumbs, enabling them Vl
to grasp objects well. Primates form
two main groups: the lower primates, ~
or prosimians, including lemurs, bush-
babies, and tarsiers; and the higher m
primates, or monkeys and apes.
;;D
Humans are primates: Recent
investigations suggest that only about ooOJ
one percentof the human genome dif-
fers from that of chimpanzees. Socially A
and physically, we seem to be most
like the bonobo. Chimps, bonobos, significant intelligence, but relative to regions of Africa, Asia, and South
and other primates-and a number body size, humans have the largest America. Among the higher primates,
of other mammal species includ- brain and the greatest surface area monkeys are classified as Old and
ing elephants and dolphins-exhibit of the cerebral cortex, an anatomical New World monkeys, based on range
difference that results in distinctive and physical characteristics. Apes'
functions such as language . distinguishing features include upright
posture, shorter spine, no tail- and
Wild primates live in rain forests, profound differences in intelligence.
mainly in the tropical and subtropical

•;

Placenta: Organ in most mammals that develops in the uterus along with a fetus to mediate metabolic exchange. I Genome: All the genetic

content contained within an organism, made up of molecules of deoxyribonucleic acid (DNA).

EGGS, POUCHES, WINGS: EXCEPTIONAL MAMMALS

Monotremes and marsupials present THE PLATYPUS, a mono- THE KANGAROO symbol- THE FLYING FOX BAT of
exceptions to certain mammalian treme, has a genetic code as izes Australia-the continent the Philippines can have a wing-
rules. Like reptiles and birds, mono- mixed up as its physical traits. with the most marsupials. span more than five feet wide.
tremes lay eggs; but like mammals, fe-
male monotremes nurse their young.
Marsupials give birth to extremely im-
mature young that complete their de-
velopment in a pouch or fold of skin,
complete with a milk source, on the
mother's body.

Bats are the only mammals that
truly fly. Flying squirrels simply glide.

FAST FACT In Mozambique, trained giant pouched rats detect explosives and land mines.

":OR MORE -ACTS ON

TROPICAL RAIN FORESTS see Forests: Rain Forests, CHAPTER 5, PAGES 198·9

+

UNUSUAL REPRODUCTIVE STRATEGIES AMONG ANIMALS see Spiders & Their Kin, CHAPTER 4, PAGES 154·5, & Animal Curiosities, CHAPTER 4, PAGES 170·1

with a long fishlike tail. Thus may have

SEA MAMMALS begun the legend of the mermaid, re-
flected in the class name for manatees
and dugongs-Sirenians. These large,

slow mammals with vestigial parts

from their land-based ancestors graze

W168 hales, dolphins, and por- toothed whales, orcas hunt in pods sea grasses and other plants in tropical
I poises are sea mammals and consume fish as well as other ma- and subtropical waters.
i:;:
known as cetaceans. rine mammals. Sea otters, relatives of the wea-
«
w
Some scientists believe these animals Baleen whales represent the sea's sel, inhabit the Pacific coastal waters
oz descend from a land-dwelling ances- largest creatures, although they feed of North America and Asia. They

W tor that resembled a small semiaquatic on tiny prey such as plankton. Bony, lack the layer of blubber that other
l.L

--' deer. Over time, bodies became meshlike plates hang from their top sea mammals have for warmth but

a:: streamlined, rear legs were lost, front jaws and filter the prey from ingested compensate with the thickest fur of

o::J legs became flippers, and a powerful, water. The blue whale can take in up any mammal. Their numbers have de-
l.L
fluked tail developed. to 8 tons of food each day. clined drastically due to the fur trade.
a::
w
I- Cetaceans spend their entire lives When sailors of yore glimpsed Many species of sea mammals ap-

«0.. in the water. They form two groups, the manatee in warm, murky tropical pear on the endangered species list.
I
based on how they feed: toothed waters, their eyes sometimes tricked Sea otters carry protected status in the
u

whales and baleen whales. Among the them into seeing a beautiful maiden United States.

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THE BOTTLENOSE DOLPHIN, its face appearing to wear a perpetual smile, can reach swimming speeds of up to 18 miles an hour.

FAST FACT The Weddell seal dives to 1,900 feet and can stay underwater for up to an hour.

FOR MORE FACTS ON

OCEAN DYNAMICS see Water: Oceans. CHAPTER 3, PAGES I 12·5

+

THE EARTH'S MANY UNDERWATER HABITATS see Aquatic Biomes. CHAPTER 5, PAGES 212·3

SEA OTTERS AND THEIR TOOLS

One of the smallest sea mammals, the a clam or other mollusk to the sur- CALIFORNIA'S SEA OTTERS feast on 169
sea otter has mastered the shallow face along with a rock. Floating on its snails, urchins, and abalones, now hard to find.
coastal waters of the northern Pacific back, it rests the rock on its chest and »z
Ocean. It lives most of its life in the wa- repeatedly bangs the clam against the the ways of the ocean. To keep her
ter, where it feeds on sea urchins, aba- rock until it opens. After the meal, the young from floating away, a mother will Vl
lone, mussels, clams, crabs, snails, fish, sea otter will roll over to wash bits of wrap kelp around herself and her pup.
octopus, and other sea creatures. shell and food off its fur. ~
. .- • - .
The sea otter belongs to an ex- Mothers raise their young totally m
clusive club of tool-users that includes offshore. A mother's body serves as a
only a small number of animal species bed, playpen, dining room, and diving ;;D
such as primates, elephants, and some platform for the young pup as it learns
birds. Diving more than 300 feet to ooOJ
obtain food, the sea otter may bring
A

WHAT HAPPENS WHEN A BLUE WHALE DIES?

The largest animal species, the blue whale can weigh 200 BLUE WHALE REMAINS on King George Island, Antarctica, undergo
tons. When a blue whale dies, other animals may feast on a transformation different from those that sink to the ocean bottom.
its remains for more than a century.

When the carcass sinks to the ocean floor, it is first
swarmed by mobile scavengers such as sleeper sharks,
hagfish, and king crabs who nibble away at soft tissue-for
up to a decade. When they finish, worms, snails, clams,
and limpets settle in on the lipid-rich carcass for another
ten years or so. Joining them are recently discovered gut-
less zombie worms that bore into the bones and mine the
lipids, assisted by bacteria inside their bodies.

Then more clams, snails, crustaceans, and worms
feed on sulfides released by bacteria that have invaded the
bones of the carcass. This stage may last a hundred years.
Even after all the nutrients are depleted, the blue whale's
crumbled carcass proVides a reeflike home for filter feeders.

•:

Plankton: From Greek planktos. "wandering" or "drifting." Marine and freshwater organisms that exist in a drifting, floating state. / Vestigial : From

Lati n vestigium, "footprint" or "trace." A small or partially developed body part that remains from a fully developed example in an earlier genera-
tion of a species or earlier stage of an individual organism.

":OR MORE -ACTS ON

THE NATURE OF BACTERIA & RELATED ORGANISMS see Bacteria, Protists & Archaea. CHAPTER 4, PAGES 148-9

+

WHALES & THEIR MIGRATION PATTERNS see Migration. CHAPTER 4, PAGES 172-3

w he animal kingdom is extraordinarily diverse.
Many species display physical features or
5 behaviors so unusual or specialized that they
raise the question why. No matter how strange,
l/) comical, or exaggerated these animal features
seem to us, they usually serve the species in some way
z relevant to day-to-day survival or the drive to reproduce.

<{ Much colorful animal behavior occurs Throughout the world, there are
during mating. Many birds and fish extremophiles-animals that survive
LAND ANIMAL WITH BIGGEST BRAIN take elaborate measures to appeal to extreme conditions. Acidophiles pre-
Elephant / 13 pounds 4 ounces the opposite sex: painstaking collec- fer acidic environments; alkaliphiles
tion and construction projects com- prefer alkaline. Anaerobes grow
HEAVIEST BIRD bined with flamboyant bodily displays without oxygen. Halophiles require
Male ostrich / 343 pounds and dancelike movements. Usually high concentrations of salt. Hyper-
the males mount the display and the thermophiles thrive in temperatures
BIRD WITH LARGEST WI N GSPAN females choose the most impressive. of 176°F and above. Toxitolerants
Great white pelican / 14 1 inches The reward? The winning male's ge- withstand toxic elements. Xerophiles
netic line survives and proliferates. grow in low moisture.
LONGEST SNAKE
Royal python / 35 fee t

HEAVIEST TERRESTRIAL ANIMAL
African e lephant / 7,500 pounds

LARGEST MOTH OR BUTTERFLY
Atlas mot her / I 1.8-inch w ingspan

MOST OFFSPRING
Prairie vole / 17 litters, 150 you ng a year

FOR MORE FACTS ON

CHEMICAL CONSTITUENTS OF PLANET EARTH see Earth's Elements, CHAPTER 3, PAGES 90·1

+

THE DIVERSITY OF PLANT & ANIMAL SPECIES see Biodiversity. CHAPTER 4, PAGES 174-5

THE BOWERBIRD: CHECK OUT MY CRIB

In many bird species, the male sports A MALE BOWERBIRD (right) puts on a show for a female, tucked inside a grassy bower in 171
brighter and more elaborate plumage the Australian bush. Once this male fin ishes, the female may visit another. Research suggests that
than the female. The fancier feathers mating decisions include assessment of the decorations collected by the male in his bower. »z
serve as a means of getting noticed and
attracting females as mates. Male bower- caps, straws, and lids, are prized . Blue bower cataloged by a researcher even Vl
birds of Australia and New Guinea lack seems to be a favored color. One included a prosthetic glass eye.
eye-catching plumage, but they increase ~
their chances of success by construct-
ing complex and often highly decorated m
bowers in which to woo the females. In-
terested visitors are treated to a full mat- ;;D
ing display that furthers the cause.
ooOJ
Male bowerbirds choose natural
objects for decorating their bowers, A
such as silvery leaves, flowers, berries,
and shells, but they will also seek out nc
and add manufactured ones to their
displays. Plastic bits, including bottle ;;D

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•:

Phenols: From Greek phoinein. ··to shine..· because they were first used in production of gases for il lumination. A class of organic compounds
with a hydroxyl group attached to a carbon atom in a ring of an aromatic compound; similar to alcohols. they are highly acidic.

THE BOMBARDIER BEETLE: DON'T COME CLOSE

Many animals have developed defen- flexible abdomens. They produce the
sive features, but the bombardier bee- irritant as needed, mixing hydrogen
tie packs a wallop unlike any other. peroxide and phenols in an enzyme
chamber, where oxidation produces
Just half an inch in length, these heat and an explosive pop.
insects live under rocks and logs and
feed on the larvae of moths and other A BOMBARDIER BEETLE cannot easily
insects. When disturbed, they blast take to flight when attacked, and so it protects
out irritating chemicals from their itself against predators by spraying.

www.p.bs.orgl.wgb/.nova/cavesextreohiles.ht I

":OR MORE - ACTS ON

THE WIDE ARRAY OF INSECT SPECIES see Insects. CHAPTER 4, PAGES 150-1

+

VARIETIES OF BIRDS & FEATURES USED TO IDENTIFY THEM see Birds. CHAPTER 4, PAGES 164-5

ARCTIC TERN
Between northern Canada & Antarctica

Round -trip 22,000-30,000 miles
90 days each way

172 CARIBOU

I "Porcupine herd": Between Yukon/Alaska

i:;: & the Arctic Circle
« Round -trip a bout 800 miles
ow
Total distance traveled can exceed 3,000
z miles per year

W

LL GRAY WHALE
---' Between Baja Mexico & the Arctic Circle

a:: Round-trip 10,000- 14,000 miles

o::J 2-3 months each way
LL

a:: RUBY-THROATED HUMMINGBIRD
w Between Mexico/ Panama & northern
«I-
U.S./Canada
"-
I Roun d-trip a bo ut S,OOO miles
U In SOO-mile stretches, 18-22 ho urs each

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5 ome animal species make epic Journeys over waters where the predators lie in wait

l/)

«z extraordinary distances as part of their annual rou- for one to stumble and be separated

from the herd. As salmon return to

tine. They migrate to escape very cold or very hot their spawning grounds, they swim

weather, to leave a dry place for a wetter one, to vulnerably near the paths of grizzlies,
find more food, and to return to a favored place to who only have to wade into rivers to
reproduce and raise young. Migrating animals may change lati- grab them. Migration also depletes fat
stores, as many species forgo eating

tude, moving north to south, or altitude, moving up or down a while on the move.
mountain, for example, with the changing seasons. Sometimes In complete migration, all the
migration is nomadic-simply a search for new food sources.
members of a species relocate season-
ally. In partial migration, many but not

all members move. In irruptive migra-

Birds, insects, fish, and mammals mi- Migration is a dangerous under- tion, members of a species may move

grate. Even some crustaceans do: taking. Birds on the wing have to battle in some years and stay put in others,

The spiny lobster migrates Significant the elements and avoid predators such depending on such factors as food sup-

distances across the floor of the Ca- as hawks while they keep their bodies ply. The snowy owl, for example, may

ribbean Sea by forming a conga line aloft for days. Wildebeest making their move south of its normal range when

of creatures attached loosely to each annual migration in search of greener populations of lemmings, its food

other by their front legs. pastures must cross crocodile-infested source, drop in Canada.

FOR MORE FACTS ON

THE PHENOMENA THAT CAUSE SEASONS see Dividing Unes: Equator & Tropics. CHAPTER 3, PAGE 37

+

THE HISTORY OF HUMAN MIGRATION see Human Migration. CHAPTER 6, PAGES 220-1

HOW DO THEY KNOW WHEN AND WHERE TO GO?

Why does migration happen when it 173
does, and how do the various species
know the routes? Animals can easily »z
sense the changing seasons. They note
shorter daylength in fall at many lati- Vl
tudes, for example, and they become
immediately aware when food sup- ~
plies dwindle. Sometimes too many
animals congregating in the same area m
triggers the need to move on.
;;D
But how do they know the route
to follow? There are several pos- ooOJ
sible answers. Many species inherit
the knowledge of the routes from A
their parents genetically. Some bird
species use the su n and the stars to WILDEBEEST OF THE SERENGETI migrate northwest from grass plains, crossing the
orient themselves as they fly. And a Grumetic River and traveling into Kenya's Masai Mara, where they cross another crocodile-
wide range of species make use of the infested river to reach the Mara grasslands in late autumn. They return to breeding grounds in
Earth's magnetic field for navigation. the spring, completing the circle that they travel.

Sea turtle hatchlings emerge on appear to be using the geomagnetic geomagnetic energy, and a patch of
moonlit beaches, head for the sea, and field for orientation. A recently identi- nerve cells in the brains of Zambian
join the regular migration route. They fied molecule in the brains of birds may mole rats is thought to process mag-
be a chemical connection for detecting netic information for navigation.

•• •• • • ••

MONARCH MIGRATION

Each fall millions of fragile monarch miles in a year. They spend the win-
butterflies undertake an amazing ter resting and conserving fat stores in
journey. They travel from southern their southern locations.
Canada and the northern United
States to the mountains of Mexico When spring comes, monarchs
and the coast of California, covering head north, laying eggs along the way.
up to 180 miles a day. Some monarchs The eggs hatch , turning into caterpil-
make a round-trip and travel 4,000 lars and then butterflies that will join
the migration, following a route they
IN MEXICO, a 217-square-mile preserve have never traveled before. Those
now protects the southernmost habitat of that complete the round-trip migra-
migrating monarch butterflies. tion expire after mating.

FAST FACT The sooty shearwater migrates 40,000 miles a year, between the Southern and Northern Hemispheres.

":OR MORE -ACTS ON

THE LIFE CYCLES OF BUTTERFLIES & MOTHS see Insects: Butterflies & Moths. CHAPTER 4, PAGES 152·3

+

EARTH'S GRASSLAND & SAVANNA BlOME see Grassland & Savanna. CHAPTER 5, PAGES 206·7

w n the natural scheme of things, the Earth harbors tens
of millions of plant and animal species, although we
5 have identified and given names to slightly less than
two million of them. Biodiversity refers to the num-
l/) ber and variety of species and natural communities in
a geographic area, and it directly correlates with the eco-
z logical health of a region. No plant or animal species op-
erates In a vacuum ; each IS part of an ecological system.
<{ GIANT MOA / Last seen in 1500
By nature, these systems are built Biodiversity knows no political
AU ROCH / Last seen in 1527 on a resilient web of interacting or- boundaries, as nature does not recog-
ganisms. When connections break nize political distinctions. The rich bio-
CHINESE ELEPHANT / Last seen in 1530 down-when imbalances develop due diversity of our planet has long been
to species endangerment or habitat under threat, and any successful solu-
DODO / Last seen in 1681 destruction-the system becomes vul- tion will be an international one. The
nerable to further weaknesses, making richness and livelihood of all our planet's
ATLANTIC GRAY WHALE / Last seen even naturally occurring disturbances biological species represent a heritage
in 1750 hard for remaining species to tolerate. and responsibility of all Earth's citizens.

STELLER'S SEA COW / Last seen in 1768

SPECTACLED CORMORANT / Last
seen in 1832

QUAGGA / Last seen in 1883

PORTUGUESE IBEX / Last seen in 1892

RIGHT WHALE / Last seen in 1900

PASSENGER PIGEON / Last seen in 19 14

FOR MORE FACTS ON

orGEOLOGIC & BIOLOGICAL EVOLUTION see Ages the Earth. CHAPTER 3, PAGES 94·5
+

THE EFFECT OF HUMAN CULTURE ON NATURE see Human Impact. CHAPTER 5, PAGES 214-5

NON-NATIVE SPECIES: EARTH'S INVASIVE ALIENS

The introduction of non-native spe- Tokyo 175
cies can threaten biodiversity, but it
has gone on since human migration Pacific; »z
began. In North America, non-native O cean
plants and animals include starlings, Ul
dandelions, earthworms, and honey- Pac ifi c
bees. Some species work out in the O cean ~
long run; introduced agricultural crops
and animals provide important food Projected Status of S OUTH , m
sources. But other species overtake
native species, having an irreversible Biodiversity, 1999-2018 AMERICA Indian ;;D
effect on flora and fauna. Oc e an
Critical and endangered ooOJ
Not all invasive species are delib-
erately introduced: weed seeds may o Threatened A
arrive among crop seeds, for example, o Relatively stable/intact
or organisms may be discharged when OJ
ships empty tanks of ballast water. ANTARCTICA
o
English ivy was likely introduced CRITICAL AND ENDANGERED AREAS of biodiversity appear in every continent. Leading
to North America for sentimental causes of extinction are loss of habitat and the introduction of non-native plants and animals. o

reasons. It spreads aggressively, and its and can add considerable weight to <
vines smother a host tree's limbs, pre- a host, making it more likely to blow
vent sunlight from reaching its leaves, over in a storm. m

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E. O. WILSON I SOCIOBIOLOGIST

Edward Osborne Wilson (b. 1929) was from the start an avid entomologist. At 13,
he came upon the first known colonies of fire ants in the United States, near the
docks of Mobile, Alabama. Ants became his specialty in his studies and as a profes-
sor of biology at Harvard. He used his expertise of ant physiology and social be-
havior to develop pathbreaking theories, often collaborating with others. He is best
known for a general theory he called sociobiology, which proposes that behavioral
patterns over time can influence genetics. An ardent ecologist and conservationist,
Wilson heads the Biodiversity Foundation, an organization he founded to safeguard
the planet's astounding but ecologically fragile variety of life-forms and habitats.

":OR MORE -ACTS ON

VARIETY OF LIFE-FORMS ON EARTH see Life Begins, CHAPTER 4, PAGES 130-1, & Life-forms, CHAPTER 4, PAGES 132-3

+

INTERNATIONAL TRADE & COMMERCE see Commerce, CHAPTER 6, PAGES 254-7

Human actions have sped up the

EXTINCTION process of extinction through habitat
degradation, hunting, fishing, collect-
ing, and other activities. This is not

just a recent phenomenon. The disap-

pearance of megafauna such as mam-

E176 xtinction, the permanent loss of a of the evolutionary process and often moths in the Americas coincided with
I species of plant or animal, occurs ties in to major environmental im- the appearance of humans there.
i:;:
when a species fails to reproduce pacts. Such a case likely occurred in Clearly, however, human actions
«
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at replacement levels and ultimately the Cretaceous period 65 million years have caused or hastened extinctions
oz dies out. Extinction often comes with ago, when an asteroid impact caused in recent centuries at a rate up to a

W environmental change. Inability to adapt catastrophic climate change, leading to thousand times higher than expected.
LL

---' to changes, say, in climate or food sup- the extinction of dinosaurs and many The International Union for Conser-

a:: ply can force a species either to die out other land and sea species. Some sci- vation of Nature (IUCN) estimates

o::J or to evolve into a new species. entists think these mass extinctions that more than 15,000 species cur-

LL Extinction serves as a natural part occur at 26-million-year intervals. rently are threatened with extinction.

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SOME SPECIES are known only from fossil remains, such as the mammoth (right), whose bones are displayed at Morrill Hall in Lincoln, Nebraska.

FAST FACT One in every four mammals faces a high rISk of extinction In the near future.

FOR MORE FACTS ON

THREATS TO PLANET EARTH see Threatened Planet. CHAPTER 3, PAGES 122-7

+

THE EFFECT OF HUMAN CULTURE ON PLANET EARTH see Human Impact. CHAPTER 5, PAGES 214-5

DINOSAURS: CELEBRITIES OF EXTINCTION

Dinosaurs dominated life on Earth for some 135 million years, 177
from their beginnings in the Triassic period 200 million years ago
until their abrupt exit during the Cretaceous period, more than »z
65 million years ago. They flourished during the Jurassic period,
when there were only two basic continents, but by the begin- Vl
ning of the Cretaceous period, 145 million years ago, they in-
habited a seven-continent planet-albeit a warmer and wetter ~
one where many species, both plant and animal , were gigantic.
m
Based on the evidence studied by paleontologists, dino-
saurs fell into two basic physiological categories: those with ;;D
bird hips and those with lizard hips, determined by the angle
at which the pelvis tilted. Most had long tails; most laid eggs. ooOJ
Dinosaurs could be either carnivorous or herbivorous. Little is
known about their temperature-regulating mechanisms. A

A catastrophic event occurred at the end of the Cretaceous m
period, believed to be agiantasteroid thathitthe Yucatan Peninsula
and formed the Chicxulub crater, still recognizable today. Such an X
event would have caused huge environmental changes leading to
mass extinctions. Yet dinosaurs seem to have been on the decline -I
for 20 million years before that. In any case, by the beginning of the Z
Cenozoic era, about 65.5 million years ago, dinosaurs were history.
n

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DINOSAUR SPECIES continue to emerge from the prehis-
toric past, as paleontologists unearth fossil evidence for ever
new evolutionary variations. Styracosaurus, for example, the
horned dinosaur at lower right in this fantasy assemblage, was a
rhinoceros-size herbivore that may have blushed, its blood filling
and reddening the fleshy frill above its forehead .

FAST FACT Passenger pigeons, now extinct, once migrated across the United States in flocks of up to two billion.

CAN SPECIES EVER COME BACK?

OccaSionally a species considered ex- Bird enthusiasts live in hope of THE IVORY-BILLED WOODPECKER
tinct reappears. Recently a rare giant the same outcome for the ivory-billed was painted by John James Audubon in the
turtle believed to be extinct in the wild woodpecker, last photographed in early 19th century, but since then the bird has
was found in northern Vietnam. The northeastern Louisiana in 1938 and disappeared and possibly become extinct.
Swinhoe's soft-shelled turtle, which can last reliably sighted in 1944.
weigh up to 300 pounds and live for
more than 100 years, was discovered It lived in the southeastern forests
and photographed by zoologists. A of the United States and the upland
second sighting in southern China has pine forests of Cuba. It is presumed
been confirmed, so the species likely extinct by many ornithologists, but
has survived a brush with extinction. sightings in 2004 and 2005 have given
bird lovers cause for optimism.

":OR MORE -ACTS ON

DINOSAURS & WHY THEY BECAME EXTINCT see Ages of the Earth, CHAPTER 3, PAGE 95

+

SPECIES FACING POSSIBLE EXTINCTION see Biodiversity: Threatened Species, CHAPTER 4, PAGES 178-9

THREATENED SPECIES

S178 ome people see a trade-off of the large umbrella organizations Across all their habitats, populations
I between protecting nature and is the International Union for Con- of gorilla, chimpanzees, bonobos, and
i:;: orangutans have declined dramatically
advancing economically; they of- servation of Nature (IUCN), head- in recent decades. The great apes are
« currently under siege from poachers,
w trophy hunters, and tribal peoples
ten view these as mutually exclusive. quartered in Gland, Switzerland. The seeking bushmeat; from pathogens
oz Yet we all benefit from biodiversity. IUCN serves as a global clearinghouse such as the Ebola virus; and from
general habitat loss and degradation,
W Environmental stewardship and the for information on all threatened ani- caused by encroaching human devel-
l.L opment. As a result, many of our clos-
est evolutionary kin may soon carryon
--' promotion of biodiversity is part of an mal and plant species. It evaluates and their lines only in the confines of zoos
and conservation research centers.
a:: overall global strategy to reverse many assesses the plight of thousands of
THE BALD
o::J of the potentially disastrous trends species each year and publishes the EAGLE:
l.L A SUCCESS
facing us in the 21 st century, including Red List, which is the standard refer- STORY
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«0.. Worldwide, many organizations One of the most threatened
I
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the cause of threatened species. One nearest to our own: the great apes.

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PROPAGATING ITS KIND, an adult bald eagle brings food to a chick, first of two to hatch in a Just a few decades ago, the United
nest of sticks and grasses built high in Newfoundland treetops. States stood in danger of lOSing its na-
tional bird. In 1963, only 417 breeding
pairs of bald eagles were known to in-
habit the lower 48 states. Hunting and
the use of the pesticide DDT were
both to blame. DDT exposure caused
the eagles to lay eggs with shells so thin
the unborn birds did not survive.

DDT was banned in 1972. The bald
eagle was placed on the endangered
species list in almost all states in 1978.
Today, there are almost 10,000 nesting
pairs in the lower 48 states. And in June
2007, the U.s. government removed
the species from the threatened list.

FOR MORE FACTS ON

THREATS TO PLANET EARTH see Threatened Planet, CHAPTER 3, PAGES 122·7

+

PRIMATE SPECIES & THEIR RELATIONSHIP TO HUMANS see Mammals, CHAPTER 4, PAGE 167

THE POLAR BEAR: VICTIM OF GLOBAL WARMING

In May 2008, the United States added A POLAR BEAR LEAPS across gaps in the pack ice in Norway's Northeast Svalbard Nature 179
the polar bear to the list of threat- Preserve. As polar ice floes melt and shrink, polar bears are losing precious habitat. In 2008 the U.S.
ened species protected under the declared polar bears a threatened species, citing sea ice loss due to global warming as the cause. »z
U.S. Endangered Species Act. Activ-
ists had supported the listing for a Vl
number of years, recognizing that the
polar ice cap was melting at even a ~
greater rate than predicted-with
new estimates that it might melt com- m
pletely by 2099.
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stage their hunting of ringed seals and ooOJ
other prey, so the loss of the ice poses
a distinct threat to their survival. A

While a robust male polar bear -I
can measure I I feet tall and weigh I
up to 1,200 pounds, there is evidence
that the species is losing its vigor and ;;D
suffering a decline in size. There has
also been a noticeable decline in the m
survival rate of cubs, which usually are
born as twins in the winter. ~

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THREATS TO SPECIES ON EVERY CONTINENT

Biodiversity is decreasing at a rapidly increasing rate. Some 1,200
fear that as many as a quarter of the world's species could
be lost in the next quarter century. Africa Australia/Oceania North America
Europe South America
Continents around the world are experiencing extinc- Asia
tion differently. Asia in particular stands to lose many spe-
cies, particularly mammals, birds, reptiles, and fish . Species
are experiencing extinction because of loss of habitat and
introduction of non-native plants and animals. Both effects
correlate with high human populations.

AS THE 21 ST CENTURY BEGAN, every type of animal was facing the o Birds Reptiles Amphibians Fishes M ollusks Other
threat of extinction to one or more of its species. Mammals *(6%) *(1 00 %) *(6 %) *(3%) Invertebrates
*(1%)
*(90%) *(100%)

"Percent assessed

FAST FACT International fisheries discard some 30 million tons of aCCidentally caught animals each year.

":OR MORE -ACTS ON

PLANTS & ANIMALS THAT LIVE IN EARTH'S ICIEST BIOMES see Tundra & Ice Cap, CHAPTER 5, PAGES 210-1

+

THE WORLD'S CONTINENTS in Africa. Asia, Europe, Australia & Oceania, North America & South America. CHAPTER 9, PAGES 360-1, 378-9, 394-5, 408-9, 414-5, 424-5

180

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HOTTEST INHABITED PLACES
Djibouti, 86.0°F

Timbuktu, Mali, 84.r F
T irunelevi, India, 84.r F
Tuticorin, India, 84.7°F

COLDEST INHABITED PLACES
Norilsk, Russia, 12.4°F
Yakutsk, Russia, 13.8°F

Yellowknife , Canada, 22.3 °F
Ulan-Bator, Mongolia, 23.9°F

WETTEST INHABITED PLACES
Buenaventura, Colombia, 265.47 in / yr

Monrovia, liberia, 202.0 I in/yr
Pago Pago, American Samoa,
196.46 in/yr

DRIEST INHABITED PLACES
Aswan , Egypt , 0.02 in / yr
Luxor, Egypt, 0.03 in/ yr
Arica, Ch ile, 0.04 in/ yr

o'o"

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~ day-to-day shifts at ground level
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« product is what we call weather: the day-to- smooth out higher in the atmosphere,

day changes in the quality of the atmosphere where the air is cold and "thin," a

near the surface of the Earth. Fundamentally, term referring to lower oxygen lev-

els. The highest winds that shape

weather is caused by the sun, which heats the air at the weather are the jet stream air cur-

planet's bulging equatorial regions more than at either Pole . rents, which roar around the globe

five to nine miles above its surface

Because hotter air rises and cooler the formation of clouds, and eventu- at speeds of up to a hundred miles

air falls, the difference in temperature ally precipitation. per hour.

across the planet causes masses of air Weather is the result of a global The effects of humidity-another

to begin to move. We feel that moving system of moving air and moisture, word for the saturation of air with

air as wind. The movement of the air but it can also be shaped by local evaporated water-can be felt at

becomes even more dynamic because features such as mountain ranges or warmer temperatures. Cooler air has

of Earth's rotation, while the steady nearby bodies of water. Weather a lower saturation point than warmer

evaporation of surface water leads to occurs only in the lower atmosphere. air. As warm, water-soaked air mole-

cules rise, they also cool. Their satura-

FAST FACT lightning can reach temperatures of around S4,OOO°F. tion point drops. Eventually the excess

FOR MORE FACTS ON

THE POLES, THE EQUATOR & THE TROPICS see The Poles. CHAPTER I, PAGES 34-5, & Equator & Tropics. CHAPTER I, PAGES 36-7

+

THE FORCES ON EARTH THAT CREATE WIND see Wind. CHAPTER 3, PAGES 106-7

water condenses into clouds and falls in air pressure-which can be thought prevent moisture from rising, and are
back to Earth. of as the weight of the air pressing usually associated with clear skies. In
down on the ground-often herald a low-pressure systems, rising air draws
Atmospheric pressure is another change in the weather. High-pressure moisture up with it, forming clouds as
factor watched closely by scientists systems bring air toward the ground, the air cools.
who monitor the weather. Changes

TYPES OF CLOUDS 183

Clouds, which are condensed water vapor, are one of the »z
most visible marks of the weather. They form in distinctive
patterns and often give a quick clue to what weather might Vl
happen in the near future.
~
HIGH-FLYING CIRRUS CLOUDS form from ice crystals four miles
above the planet's surface. and their sparse, wispy streaks are usually a sign m
of clear weather.
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STRATUS CLOUDS are flat, broad, and close to the ground, and they
usually prompt observers to grab a raincoat. The lowest stratus clouds touch ooOJ
the Earth in the form of fog.
A
NIMBOSTRATUS CLOUDS stretched out like a blanket usually fore-
shadow extended precipitation. ~

CUMULUS CLOUDS can be playfully puffy components of a high-pres- m
sure system, but they can also build into towering cumulonimbus thunder-
heads, accompanying a squall or thunderstorm. ~

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Front: The boundary between large air masses of differing temperature and moisture content. I Lightning: The violent leveling of an electrical

imbalance between the Earth and a storm cloud.

HOW DOES TOPOGRAPHY AFFECT WEATHER?

Windward
(wet)

Wind

Pacific
Ocean

Coa st Si erra Nev ada

MOUNTAIN RANGES BLOCK AIR MOVEMENT, as on the California coastline (above), .c.=OO=I=:::IIwiiiaiirimi.~ Temperature variations as
where precipitation collected from the ocean falls in the Sierra Nevada, leaving the leeward slopes dry. ~ air moves over mountains

":OR MORE -ACTS ON

THE CONTINENTS ON PLANET EARTH see Continents, CHAPTER 3, PAGES 84-5

+

HOW ELEMENTS AFFECT THE SHAPING OF EARTH'S LANDFORMS see Landforms: Taking Shape CHAPTER 3, PAGES 100·1

abies like temperature and pressure

PREDICTIONS were developed well before then,
but the development of the telegraph
provided a missing link in the 1800s-

the ability to assemble data quickly

from different geographic locations

K184 nowing the weather in advance short-term predictions and can moni- and compare it for patterns of change.
is an obvious benefit-for farm- tor local conditions closely enough to At Washington's Smithsonian In-

ers wondering about rainfall, give advance notice of when torna- stitution, Joseph Henry was preparing

sailors wondering about navigation, or, does, hailstorms, or other dangerous daily weather maps using telegraphed

in modern times, pilots and passengers events are likely to occur. reports by 1849; early meteorologists

V1 wondering whether inclement weather Though casual observation can at the Cincinnati Observatory began
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~ may affect air travel. With data gath- provide an idea of where a weather preparing forecasts in 1869. Two years
L ered from networks of balloons, sat- system is heading, systematic analysis later, the U.s. Army Signal Corps be-
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U ellites, radar, and other equipment, was not possible until the mid-19th gan operation of the first network of

meteorologists can create reasonable century. Tools to measure basic vari- national weather stations.

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«0.. naked eye for observation. A global

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o'o" attached to them-were launched

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a: each day, feeding back data about at-

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pening at ever higher heights. That

system is in place today, with balloons

launched every 12 hours from some

700 locations around the world.

Coupled with data from about

25,000 ground stations, this informa-

tion goes into supercomputers that,

using complex models, forecast the

weather for the coming days. Since

1960, the system has been augmented

by satellites that give a view of cloud

patterns and the movement of storms.

A WEATHER BALLOON drifts upward from an icebreaker in the Bellingshausen Sea, Antarc- Radar supplements the readings with
tica, released on its mission to sense and deliver data on atmospheric pressure and temperature. more local data.

FAST FACT The first known photograph of a tornado was taken on August 28, 1884, near Howard, South Dakota.

FOR MORE FACTS ON

WIND CHARACTERISTICS & DYNAMICS ON PLANET EARTH see Wind. CHAPTER 3, PAGES 106·7

+

WEATHER & CLOUD FORMATIONS see Weather. CHAPTER 5, PAGES 182·3

WHAT IS DOPPLER RADAR?

By tracking changes in the speed and A DOPPLER RADAR ANTENNA tracks storms in the Texas Panhandle. Weather radar tools 185
direction of wind and precipitation, sense precipitation's intensity and motion; the information is projected onto maps for the general
Doppler radar helps detect when public, using colors to distinguish different types of precipitation. »z
dangerous rotational patterns are
developing- precursors to things like Vl
tornadoes and hurricanes. The instal-
lation of short-range Doppler radar at ~
airports has given air traffic control-
lers the ability to know when condi- m
tions are ripe for microbursts or wind
shear, a phenomenon that has caused ;;D
planes to crash at takeoff and landing.
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Astronomers have applied the
Doppler effect- the change in the A
wavelength of light emitted by a
moving star- to show that galaxies ~
are moving away from one another.
Meteorologists use the phenomenon m
to improve their ability to warn of im-
minent weather. ~

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Cyclones: From the Greek kykloun, "whirl" or "move around in a circle." Swirling air masses that converge around low-pressure areas. often

associated with storms. I Anticyclones: Swirling air masses that converge around high -pressure areas. often associated with clear weather. I

Synoptic forecasting: General overview of changes in temperature and pressure drawn from data across a wide area.

Water vapor becomes clouds. WHAT IS RAIN?

I W_ater evaporates. Rain is one of the stages in the planet's
'-"" ~- -,, " .... l .J J hydrologic cycle (also called the wa-
ter cycle) , the constant circulation of
Lake moisture through levels in Earth and its
atmosphere. Evaporation transports
Precipitation falls and River watervaporfrom land and ocean to the
atmosphere. Water returns to Earth in
runs off and into the form of precipitation. On land, wa-
the ground. ter constantly seeks lower ground and
ultimately flows into the ocean.

----

lif: National Oceanic & Atmospheric Administration www.noaa.gov

":OR MORE -ACTS ON

ASTRONOMICAL OBSERVATION METHODS TODAY see Observation: Modern Methods, CHAPTER 2, PAGES 70·1

+

WATER & THE WATER CYCLE ON EARTH see Water, CHAPTER 3, PAGES 110·1

~ torms result from imbalances- such as warm air
colliding with cold air, low-pressure areas feeding so
oo much moisture into the atmosphere that it pours
cD back as rain , or the friction of rising air creating a
static charge that gets released as lightning-and
n::: can be among nature's most violent and catastrophic events.
Thunderstorms develop when the usual pattern of rISing
w warm air becomes intensified and concentrated in a shaft.

5
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695 dead
<t:

MAY 6, 1840 1 NATCHEZ, MS
3 17 dead

MAY 27, 1896 1 sr. LOUIS, MO

255 dead

APRIL 5, 1936 1TUPELO, MS As the moisture in the cell of rising air ing cold air can translate into vicious
condenses, it releases heat that pushes winds. As electricity is discharged in
2 16 dead the air higher still. From a puffy cumu- the form of lightning, the shock wave
lus cloud, a towering cumulonimbus of thunder can be heard miles away.
APRIL 6, 1936 1GAINESVILLE, GA thunderhead can build, accumulating
203 dead moisture and electric charge until the Thunderstorms can also spawn
imbalance becomes too much to sus- tornadoes, which form when large
APRIL 9, 1947 1WOODWARD, OK tain. Rain may fall in torrents, and fall- air masses with sharply different tem-
181 dead peratures, wind directions, and wind

APRIL 24, 1908 1 LA, MS

143 dead

FAST FACT Between 700 and 1,000 tornadoes occur annually In the U.S.

THE ATMOSPHERE & ITS COMPONENTS see Eorth's Atmosphere. CHAPTER 3, PAGES 104·5
FAMOUS WIND PATTERNS FROM AROUND THE WORLD see Wind. CHAPTER 3, PAGES 106·7

speeds collide. The rising warm air may Flashes (per sq. km/year) 187
begin to spin, a process accelerated
when higher, cooler air rushes down- • More than 50 6- 9 0.4- 0.7 »z
ward. In its early stages, this spinning
mass of air is called a mesocyclone. • .30- 50 0 2- 5 . 0.1- 0.3 Vl
Under conditions, which storm re- • 10- 29
searchers cannot yet fully explain, the 0 0.8-1.9 0 Less than O. ~
spin can form into the well-known
funnel shape. LIGHTNING FLASHES AROUND THE WORLD, but some regions see more than others, m
as shown in this world map generated by NASA scientists using five years of data-a total of more
Tornado intensity is measured by than 1.2 billion intracloud and cloud-to-ground flashes-and calculating mean annual distribution. ;;D
the six-degree enhanced Fujita scale,
based on the damage caused. The Both thunderstorms and torna- Atlantic coast of the United States in ooOJ
majority rank low on the scale: They does have the effect of quickly cor- winter. When warm low-pressure sys-
grow to perhaps 600 feet wide, trav- recting differences in pressure and tems, fed by the waters off the coast A
eling at about 30 miles an hour, and temperature between air masses. of Florida, collide with cold high-
typically move no more than 6 miles Those imbalances can also give rise pressure systems fed by Arctic air, Vl
before they dissipate. to lingering storm systems, such as the result can be feet of snow or long
the "nor'easters" that howl along the spells of cold, rainy weather. o-I
The largest tornadoes may span
more than a mile, travel at speeds ;;D
of up to 70 miles an hour, and travel
as far as 300 miles. Their winds may 3:
reach 300 miles an hour.
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FAST FACT About 16 million thunderstorms and 1.2 billion lightning strikes occur annually across the planet.

WHAT TO DO IN A TORNADO

Tornadoes kill roughly 100 people or bathroom and use a mattress or A FAMILY LIES LOW, as recommended, in
each year in the United States. Most blankets for extra protection . Stay a highway underpass as a tornado rips through
die after being struck by flying or fail - away from windows, since glass may the Newcastle, Oklahoma, area.
ing debris. If a storm is approaching, fly. Anyone caught outside should lie
therefore, it's best to move to a con- low in a ditch or culvert, if possible,
fined space where the chances of be- or near a tree or pole that can be
ing struck are minimized . That means grabbed . Don't stay in a car- it may
moving to the basement and shelter- be swept away by the storm. People
ing beneath a table or workbench. If in mobile homes should relocate to
there is no basement, move to a closet more secure structures.

":OR MORE -ACTS ON

HURRICANES & TYPHOONS see Storms: Hurricones. CHAPTER 5, PAGES 188-9

+

ENGINEERING MATERIALS DESIGNED TO WITHSTAND STORMS see Physicol Science: Engineering. CHAPTER 8, PAGES 332-3

HURRICANES

T188 he collision of warm and cold wind speed in excess of 74 miles per amounts of water they dump from the
air often results in large rotat- hour. But they occur in different parts sky and push inland through a storm
ing weather systems known as of the world: The storm is called a hur- surge-a wall of ocean water. On
cyclones, low-pressure zones that can ricane if it develops over the Atlantic September 8, 1900, between 6,000

lead to days of cloudy weather and or eastern Pacific Ocean, a cyclone if and 8,000 people drowned in Galves-

V1 precipitation. When such systems de- it develops over the Bay of Bengal or ton, Texas, for example, when a 20-
W

~ velop over warm ocean water, typically the Indian Ocean, and a typhoon if it foot storm surge flooded the town in
L between 5° and 25° above the Equator, develops over the western Pacific.
the deadliest natural disaster in U.S.

--.J Strong and deadly, these storms history. In Asia, individual typhoons

U they can produce the massive storms

known as hurricanes, tropical cyclones, are dangerous not just for their winds, have claimed hundreds of thousands

w

> and typhoons. These three types of which can rage in excess of 150 miles of lives-including a storm in 1970 in

l.L

a: storm are the same-defined by a per hour, but also for the massive Bangladesh that killed 300,000 with an

w

I- estimated 30-foot surge of water.

«0.. Hurricanes, cyclones, and typhoons

I

u form as winds from different direc-

tions meet over the ocean. Warmed
'oo" by the ocean, moisture-laden, low-

cD pressure air begins to rise. As cooler

a: air rushes in, it is also warmed and hy-

w
~ drated, and it begins moving upward.
zV1
« Typically, this air movement leads to

little more than thunderstorms, but

sometimes the system will organize it-

self and begin to spin, gathering force

as it moves across warm water. Now

the system is classified as a tropical de-

pression, because of its extreme low

pressure. When its winds reach 39

miles per hour, it becomes classified

as a tropical storm. At 74 miles per

hour, it is reclassified as a hurricane

or other serious storm. While these

tropical storm systems may wander

harmlessly at sea, they often do not

A MASSIVE STORM SURGE-a wall of water pushed on land by strong winds-accompa- fully dissipate until they reach land.
The collision with land robs them of
nied Hurricane Katrina in August 2005. Reaching 20 feet above sea level, it pummeled the Loui-
siana and Mississippi coastlines and left many houses standing in water. The world's worst storm the warm ocean water that fuels them.
surge occurred in Bathurst Bay, Australia, in 1899, when a hurricane produced a 42-foot surge.

FOR MORE FACTS ON

WATER IN ALL ITS FORMS ON PLANET EARTH see Water. CHAPTER 3, PAGES 110·1

+

THE INTERACTION OF OCEANS & ATMOSPHERE IN CAUSING WEATHER see Water: Oceans, CHAPTER 3, PAGE 113

KATRINA'S LEGACY

Hurricane Katrina raked the U.s. Gulf coastline in August 189
2005. It left about 75 percent of New Orleans underwater
when levees built to protect the city from Lake Pontchar- »z
train and Lake Borgne failed . A study soon after found at
least three different types of levee breaches, some of which Vl
might have been prevented with minor design adaptations.
~
In several spots, the storm surge from the hurricane
built up above the levee's concrete wall, spilling over the m
top, eroding the supporting earthen embankment on the
other side, and eventually collapsing the wall itself. Else- ;;D
where pressure from the storm surge pushed through
the underlying soil and eroded the levee from beneath. ooOJ
Where levees of different design met, weak spots in one
led to larger breaches overall. A

SATELLITE IMAGERY OF KATRINA at 8: I5 p.m. Sunday, August I
28, 2005, reveals the intensity of the storm near peak strength. C

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CYCLONES: WHERE & WHEN?

Hurricanes, cyclones, and typhoons NORTH EUROPE PACIFIC
develop over tropical waters in sum- OCEAN
mer and autumn, when ocean temper- - A SI A
atures are warmest. The movement
of these storms is governed by global Late May-early Nov. /storms all year
and upper atmosphere winds and by peak: Aug- Sep ( 'peak: Jul- Nov
the Coriolis effect, deflections created
by Earth's rotation . PACIFIC AFRICA
OCEAN
About a hundred storms form SOUTH ATLANTIC Apr-Dec. Late Oct-May.
near the west coast of Africa every AMERICA OCEAN double peak:
year. Of those, only 10 percent actu- , - p::~eb-Mar
ally maintain their shape, travel across (Apr-Ju~~~el:-~ec
the Atlantic , and reach the coasts of OCEAN AUSTRALIA
the Caribbean and North America as
hurricanes. Late Oct-May.
peak: Jan- Feb
PREDICTABLE PATTERNS of season and
location do not reduce the terror and devasta- ANTARCTICA Typical tropical
tion that tropical cyclonic storms can cause. - cyclone tracks

Cyclone season,
peak months

":OR MORE -ACTS ON

THE DEFINITION OF TROPICAL REGIONS see Dividing Lines: Equator & TropiCS, CHAPTER I. PAGES 36·7

+

LAYERS OF THE ATMOSPHERE see Eorth's Atmosphere. CHAPTER 3, PAGES 104-5

nuclei," forming supercooled crys-

SNOW & ICE tals around bits of salt, sand, dust,
pollutants, and other material scat-
tered through the upper atmosphere.

Clouds form, and the particles of ice

continue to grow until they become

M190 OSt precipitation begins as Since colder air can hold less water, it so heavy that they fall to the Earth.
ice crystals in the cold upper eventually reaches a saturation point. What happens on the way down

reaches of cloud formations. Water vapor then begins to condense determines whether the precipita-

As warm air rises, it begins to cool. around microscopic "condensation tion reaches the ground in the form

of snow, ice, sleet, or hail-all forms

V1 of frozen precipitation that can cause

W

~ tremendous damage, even (in the

L case of snow) while offering recre-

...J

U ational opportunities for winter sports

enthusiasts.

w

> If temperatures are above freez-

l.L

a: ing near the ground, the ice crystals

w

I- melt and turn into rain. But if ground

«0.. level temperatures are below freez-

I

u ing, the crystals remain intact as they

accumulate more water vapor or

'oo" merge together to form snowflakes.

cD Sometimes, the falling ice crystals pass

a: through a band of warm air and melt,

w
~ only to freeze again if lower level tem-
zV1
« peratures are cooler. Sleet is rain that

has fully refrozen before it hits the

ground. Rain that freezes as it comes

in contact with the cooler surface of

the Earth is called "freezing rain"-a

particularly hazardous form of precip-

itation that can make driving treacher-

ous and topple trees and power lines

under the weight of the ice.

Water that freezes in the upper

reaches of a thunderstorm can accu-

mulate into large pellets of ice-hail-

stones-that can reach as much as

four inches in diameter. In addition to

being dangerous, hailstorms can cause

WINTRY WEATHER meant snowy roads, requiring careful driving and daytime headlights, in damage to crops, automobiles, and

southern Germany in January 2007. other property.

FOR MORE FACTS ON

ICE AS ONE FORM OF WATER ON PLANET EARTH see Water: Ice. CHAPTER 3, PAGES 120·1

+

PLANTS & ANIMALS THAT LIVE IN SNOW·FILLED & ICY BIOMES see Tundra & Ice Cap. CHAPTER 4, PAGES 210·1

HOW DO SNOWFLAKES FORM?

Snowflakes start as ice crystals that called sublimation. The flakes, typically flake shapes: plates, stellars, columns, 191
form high in the atmosphere, when hexagonal, are infinite in design . Their needles, spatial dendrites, capped
water vapor either condenses around individuality depends on the tempera- columns, and irregular crystals, each »z
a solid nucleus or, under even colder ture and pressure at which freezing associated with temperatures ranging
conditions, freezes directly in a process occurs. There are seven basic snow- from freezing to -50°F. Ul

~

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A

Ul

oZ

~

Qo

()
m

NEEDLES, including these crossed STELLAR DENDRITES is one of the CAPPED COLUMNS have crystals
needles, form at about -23°F. shapes visible with the naked eye. perpendicular to a central column.

WILSON A. BENTLEY I STUDENT OF SNOWFLAKES

Wilson A. "Snowflake" Bentley (1865-193 I) was a farmer by trade, but from the
snowy landscape of Vermont he drew inspiration for another calling: document-
ing the intricate and apparently non repetitive designs of snowflakes. Connecting a
rudimentary bellows camera to a microscope, Bentley took the first photographs
of snowflakes in I88s-showing them to be far more than simply frozen drops of
water. Instead, he found them to be "miracles of beauty.... Every crystal was a mas-
terpiece of design and no design was ever repeated." Over the years, Bentley pro-
duced some 5,000 photographs of snowflakes. Along with revealing their structure,
his work pioneered the field of photomicrography-using photography to reveal
what was invisible to the naked eye.

" The mysteries of the upper air are about to reveal themselves, if our hands "

are deft and our eyes quick enough. - WILSON A. BENTLEY, 1902

":OR MORE -ACTS ON

THE VARIETIES & CAUSES OF WEATHER PATTERNS ON EARTH see Weather, CHAPTER 5, PAGES 182·3

+

ADVANCES IN ELECTRON MICROSCOPY see Optics, CHAPTER 8, PAGES 336-7

HOTTEST PLACE
Dalol, Denakil Depression

Et hiopia
Ann ual average temperature:

93.2°F

COLDEST PLACE
Plateau Station
Antarctica

Ann ual average temperature:
· 70°F

WETTEST PLACE
Mawsynram, Assam

India
An nual average rainfall:

467 in / yr

DRIEST PLACE
Atacama Desert

C hile
Rainfall barely measurable

o'o"

cD eather happens from day to day, In a given area. The steady flow of
cr:
w whereas climate refers to average heat and sunlight to Earth's equatorial

~ areas, for example, yields the hot, wet
zV)
« conditions over time. Climatologists conditions associated with rain forests

look at trends over decades and cen- and other tropical regions. Toward

turies, including average precipitation, the Poles, climate tends to get pro-

gressively drier and colder.

average temperature, prevailing winds, and the average amount These general climate rules are

of sunlight received. Climate shapes the surrounding environ- affected greatly by the presence of
ment and influences both the biology and the culture of a region. mountains or nearby bodies of water.

Immediately to the north of Africa's

Climate is determined by large-scale resulting uneven distribution of sun- tropical zone, for example, precipita-

patterns and forces, beginning with light-and of temperature in the tion practically disappears across the

the position of the Earth 93 million atmosphere and throughout the arid expanse of the Sahara. The Rocky

miles from the sun, close enough to world's oceans-establishes under- Mountains in the U.S. and Canada bot-

receive a life-sustaining amount of so- lying sea current and wind patterns tle up moist air pushed inland from the

lar radiation. that, in turn, influence climate. Pacific on westerly breezes, increasing

Since Earth tilts on its axis, much Latitudinal banding, from the precipitation on the windward side of

of the sun's heat falls on the tropi- Equator outward to the Poles, plays a the mountains and creating drier con-

cal areas around the Equator. The central role in determining conditions ditions to the lee.

FOR MORE FACTS ON

THE DETERMINATION OF EARTH'S LATITUDES see Dividing Lines. CHAPTER I, PAGES 30·7

+

THE IMPORTANCE OF DIVERSITY AMONG LlFE·FORMS ON PLANET EARTH see Biodiversity. CHAPTER 4, PAGES 174·5

WHAT ARE INDICATORS OF GLOBAL WARMING?

Climatic conditions remain relatively o
constant when seen from the human
perspective, but they have changed o .../ ;~ . /ATLANTIC 193
many times over the life of the planet. 0""" /
A warming trend in the last century • OCEAN »z
raises the urgent question of whether
human activity is now changing the cli- ~o Ul
mate. The United Nations' Intergov-
ernmental Panel on Climate Change California Cold w inds over ~
shared the 2007 Nobel Peace Prize Current
for its work on climate change. warm water m
PACIFIC
The panel studied the net change OCEAN Coo l onshore ;;D
in heat entering or leaving the climate ocean winds
system and concluded that due to in- ooOJ
creased greenhouse gases like carbon Desert w inds
dioxide- up from 280 parts per mil- A
lion in pre-industrial society to 379 Warm onshore
parts per million in 200S- heat ex- Gul f 0 f ocean w inds
change had increased about 2.3 watts M exi co
per square meter since 17S0. That in-
crease- unprecedented over the last GEOGRAPHY INFLUENCES CLIMATE, as this map illustrates. Coastal areas are refreshed
when cooler air moves ashore. South and east of the Great Lakes, "lake effect" snow falls when
cold air sweeps over warmer waters. Spring and summer thunderstorms build where three types
of air mass converge: cold and dry from the north, warm and dry from the southwest, and warm
and moist from the Gulf of Mexico.

10,000 years-is leading to warmer snow pack and ice at the Poles. These
ocean temperatures, higher sea lev- climate changes could influence the
els, increased humidity, and shrinking weather worldwide.

WLADIMIR KOPPEN I CLIMATE SCIENTIST

Born to a distinguished academic family in imperial Russia, Wladimir Koppen (1846-
1940) noticed during trips to his family's coastal estate on the Black Sea how the plant
life changed as he traversed plains, mountains, and the seaside landscape. His study of
how flora was related to climate led him in 1884 to produce a map of global temper-
ature bands ranging from the Poles to the Equator. Sixteen years later he refined that
map into a mathematical formula, which defined five major climate types based on
temperature and rainfall-ranging from the intense humidity of the tropics to the cold,
dry polar caps. The system, still in use today, corresponds roughly to the classification
system of biomes that describes the world's regions based on plant and animal life.

":OR MORE -ACTS ON

THE DEFINITION OF GREENHOUSE GASES see Threatened Planet: Air, CHAPTER 3, PAGE 125

+

THE IMPACT OF HUMAN SOCIETY ON EARTH see Human Impact, CHAPTER 5, PAGES 214·5

o'o" ife on Earth exists within a complex bubble called
the biosphere, the only one so far known in the
cD universe. Extending from the floor of the ocean to
about six miles above sea level, the biosphere de-
cr: pends on the interaction of several large systems
to process energy from the sun: the atmosphere (which pro-
w vides oxygen), the hydrosphere (water in the ground and in
the oceans), and the lithosphere (the land itself).
~
Several classification systems have been according to dominant types of trees
zV) devised to organize Earth's life-forms. and grasses.
« Most take into account temperature, cli-
mate, and neighbOring life-forms within Although agriculture, urban de-
TEMPERATE FOREST a region. The basic unit is called a biome, velopment, and human population
a geographic concept that can refer to growth have altered the distribution
RAIN FOREST areas on different continents that still of plant and animal species, biome
BOREAL FOREST share similar climates, terrains, and liv- classifications are based on the living
ing things. Biomes are typically grouped things that would naturally exist in an
MEDITERRANEAN FOREST area without human intervention. The
MANGROVE

GRASSLAND & SAVANNA

DESERT & DRY SHRUBLAND

TUNDRA & ICE CAP
MARINE

FRESHWATER

FOR MORE FACTS ON

THE HISTORY AND PROCESS OF CLASSIFYING LIVING ORGANISMS see Life-forms, CHAPTER 4, PAGES 132-3

+

THE DIVERSITY OF LIVING THINGS ON EARTH see Biodiversity, CHAPTER 4, PAGES 174-9

presence of specific plants or animals contain vines and monkeys, though network that supports a wide variety
is not as important as the forms of life the individual species vary widely. of life, from minuscule bacteria to 80-
involved: The rain forests of Africa foot blue whales, and the only one so
and South America, for example, all All Earth's biomes sum up into far known in the universe.
the biosphere-a dynamic, complex

• Tropical & subtropical moist ANTARCTICA m
broadleaf forest
;;D
• Tropical & subtropical dry
broadleaf forest ooOJ

• Tropical & subtropical A
OJ
coniferous forest
o
Tropical & subtropical
grassland, savanna 3:
& shrubland m

• Temperate Vl
broadleaf &
A PALETTE OF
mixed forest
15 colors helps visualize
• Temperate
conifer forest 142 terrestrial ecoregions,

Temperate representing Earth's many
different biomes.
grassland,
savanna &
shrubland

• Flooded
grassland &
savanna

Montane
grassland &
shrubland

• Boreal forestJtaiga
Tundra

• Mediterranean
forest, woodland & scrub

• Desert & xeric shrubland

• Mangrove
Ice cap

EARTH'S MANY ECOREGIONS

Political boundaries make one set of grassland, desert, and tundra. More for instance, earn a classification all to
divisions in the world, nature another- specific classifications separate the themselves. Others cover vast areas
and conservationists suggest we ignore tropical rain forests of South America of the planet but support compara-
politics to protect biodiversity. from the temperate pine stands of tively little life- the sprawling deserts
the American South. Some biomes of North Africa and Asia, for example.
Among the various classifica- are limited in scale and unique in the These classifications are still subject to
tion systems in use, there are some life they support: Mangrove swamps, debate and reinterpretation.
broadly accepted categories. The U.S.
Forest Service divides the planet into ..• • -
four basic types of land biome: forest,

":OR MORE -ACTS ON

METHODS OF MAPPING EARTH'S PHENOMENA see Geography, CHAPTER I, PAGES 16·7, & The World in Maps, CHAPTER I, PAGES 18·9

+

SPECIFIC BIOMES see Forests, Mangroves, Grassland & Savanna, Desert & Dry Shrubland, Tundra & Ice Cap, Aquatic Biomes, CHAPTER 5, PAGES 196·213

m

3"

o'o" he world's temperate forests are characterized
by a variety of deciduous trees-oak, hickory,
cD beech, elm, willow, and others-that thrive during
the mild growing season and survive the seasonal
cr: changes common across North America, central
Asia, and western and central Europe. Temperatures in these
w areas can go below freezing during the winter months and top
90°F in the summer. The spring and summer provide a growing
~ season as long as 200 days, with perhaps six frost-free months,
during which species must store energy for the colder periods.
zV)
« Depending on temperature and rain- steady rainfall of tropical forests but
fall patterns, a temperate forest bi- cooler temperatures (though typically
RUSSIA ome can also include evergreen trees, above freezing).
2.957.203 square miles such as the coniferous pines found
throughout the U.S. It also includes The canopy in temperate forests
CANADA the temperate rain forests of the can be dense, but some vegetation
1.907.345 square miles Pacific Northwest. which have the grows at ground level. Animal life
includes small ground-dwelling
BRAZIL
1.884.179 square miles

UNITED STATES
1. 142.824 square miles

DEMOCRATIC REPUBLIC OF CONGO
671 .046 square miles

AUSTRALIA
559.848 square mi les

CHINA
503.848 square miles

FOR MORE FACTS ON

THE BIOLOGY OF SHRUBS & TREES see Shrubs, CHAPTER 4, PAGES 140·1, & Trees, CHAPTER 4, PAGES 142·3

+

THE DEFINITION OF DECIDUOUS see Plants: Shrubs, CHAPTER 4, PAGE 141

mammals such as rabbits and skunks, Leaves falling from deciduous ate forests in Europe and China were 197
large populations of deer, and pred- trees enrich the soil, which has made harvested for use in ships and build-
ators such as bobcats, wolves, and the world's temperate forest regions ings. The hardwood forests in North »z
foxes. Temperate forest animals valuable for agriculture. Timber from America were largely exhausted by
adapt to winter with thick hair for oak, elm, and other forest trees has the end of the 19th century, mean- Vl
warmth, foraging or food storage long been used in construction. Begin- ing that the world contains less forest
habits, and hibernation. ning about 8,000 years ago, temper- land now than in ages past. ~

m

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ooOJ

A

o"Tl

;;D

m

Vl

-I

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ASPEN TREES in Colorado grow tall and BLACK BEARS inhabit North American WILD SUNFLOWERS sprout in the after-
straight. Their leafy canopy prevents significant forests from Alaska to northern Mexico. They math of a fire in California, a first step toward
forest undergrowth. hibernate through cold winters. the forest's rebirth.

•

Deciduous: From the Latin decidere, to fa lloff. Tree species whose life cycles include the annual shedding of leaves. I Mycorhizae: From Greek
mykcs. "fu ngus." + rhizQ, "root." Fungi that help trees absorb nutrients more efficiently. I Vegetation profile: Collection of smaller plants and

shrubs in a forest that compete for resources beneath the trees.

WHEN DID AUTUMN COLORS EVOLVE?

Autumn leaves came into being at the start of the Ce-
nozoic era, about 65 million years ago. After that, only
equatorial areas faced the sun in a way to guarantee con-
sistently high temperatures and steady rainfall. During
much of the year elsewhere, there was not enough sun-
light to support photosynthesis, and frost proved damag-
ing to leaves. Deciduous species developed as a result,
discarding thin leaves at the growing season's end.

MAPLE LEAVES, like these on a vine maple in Washington's
Olympic State Park, display vibrant autumn reds.

":OR MORE -ACTS ON

WHY LEAVES CHANGE COLOR see Plants: Trees, CHAPTER 4, PAGE 143

+

ASIA, EUROPE & NORTH AMERICA in Asia, Europe & North America, CHAPTER 9, PAGES 378-407, 414-23

straight-trunked trees dominate the

RAI N FORESTS landscape. Under such favorable con-
ditions, trees grow so tall and lush that
they create an aboveground canopy,

which, because it blocks sunlight, lim-

its ground vegetation. Animals thrive

T198 ropical and subtropical rain for- The result is little seasonal variation in in this canopy, however. Arboreal
ests present examples of how temperature and nearly daily thunder- animals such as monkeys are typical,

a hot, steady climate promotes storms and rainfall. This climate gives and insects proliferate; insect-borne
remarkable diversity in plant growth. rise to the tropical and subtropical diseases like malaria and yellow fever

Near the Earth's Equator, trade forests, home of the world's most di- are a constant threat.

V1 winds from different directions collide verse collection of species. Despite being under intense log-
W

~ and create azone of risingairthatdraws The belt near the Equator itself ging and development pressure, the

L water up from the ground. Steady sun- includes the rain forests of South rain forest zone remains the heart of

-..J

U light aids the process through evapo- America, central Africa, and Asia- world biodiversity, home to several

ration and keeps temperatures high. evergreen areas where broad-leaved, million species including a hundred or

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BUTTRESSED ROOTS of a tropical ceiba support a huge singular column and a canopy of leaves in the Guyana rain forest. Tallest trees of the
Amazon. ceibas can reach a height of nearly 200 feet. The Maya believed a ceiba stood at Earth's center. making a connection to the spirit world above.

FOR MORE FACTS ON

THE DEFINITION OF THE TROPICS see Dividing Unes: Equator & TropiCS. CHAPTER I. PAGES 36·7

+

THE DIVERSITY OF LIVING THINGS ON EARTH see Biodiversity. CHAPTER 4. PAGES 174·5